I had leaks in the front and rear of my footwells (mostly the drivers side), and cos the skirts were blended in to the fender, I couldnt get that off to do that fix underneath the panel...So I did the job on the rear drain pipes, sorted it from coming in there, and then got about removing my bonnet to have a look around the hinges to see if anything there could be sealed up...and found this little hole
found that if you poured water down it it would go directly on to the fuse box, not good!
so stripped it all away with some wire wool, masked off all surround area (eg everything part from where the hinge goes), and sprayed it with some hammerite to stop rust getting at it again. Then stuck a shed load of silocon sealant in the hole, and cover the rest of the area that the hinge sits on with it, then bolted the bonnet back on. (carefull when removing bonnet not to snap the window washer hose like I did!) Also did the same on other side, there wasn't the hole on that side, but still stripped it, painted it, and put lots of sealant down too. This sorted the problem like 99% on the drivers side, think there may be a real tiny amount coming through if there is heavy rain, nothing to worry about though. So if you've got water in the foot well and cant remove te front fenders give this a shot.